Disordered breathing refers to a wide spectrum of respiratory disorders that involve disruption of the normal respiratory cycle. Although disordered breathing typically occurs during sleep, the disorder may also occur while the patient is awake. Unfortunately, disordered breathing is often undiagnosed. If left untreated, the effects of disordered breathing may result in serious health consequences for the patient.
Apnea is a fairly common breathing disorder characterized by periods of interrupted breathing. Apnea is typically classified based on its etiology. One type of apnea, denoted obstructive apnea, occurs when the patient's airway is obstructed by the collapse of soft tissue in the rear of the throat. Central apnea is caused by a derangement of the central nervous system control of respiration. The patient ceases to breathe when control signals from the brain to the respiratory muscles are absent or interrupted. Mixed apnea is a combination of the central and obstructive apnea types. Regardless of the type of apnea, people experiencing an apnea event stop breathing for a period of time. The cessation of breathing may occur repeatedly during sleep, sometimes hundreds of times a night and sometimes for a minute or longer.
In addition to apnea, other types of disordered respiration have been identified, including hypopnea (shallow breathing), tachypnea (rapid breathing), hyperpnea (heavy breathing), and dyspnea (labored breathing). Combinations of the respiratory cycles described above may be observed, including, for example, periodic breathing and Cheyne-Stokes breathing. Periodic breathing is characterized by cyclic respiratory patterns that may exhibit rhythmic rises and falls in tidal volume. Cheyne-Stokes respiration is a specific form of periodic breathing wherein the tidal volume decreases to zero resulting in apneic intervals. The breathing interruptions of periodic breathing and CSR may be associated with central apnea, or may be obstructive in nature. CSR is frequently observed in patients with congestive heart failure (CHF) and is associated with an increased risk of accelerated CHF progression. Because of the cardiovascular implications, therapy for respiration-related sleep disorders is of particular interest.
Disordered breathing affects a significant percentage of people. Sleep disordered breathing is particularly prevalent and is associated with excessive daytime sleepiness, systemic hypertension, increased risk of stroke, angina and myocardial infarction. Respiratory disruption can be particularly serious for patients concurrently suffering from cardiovascular deficiencies, such as congestive heart failure.
Snoring may indicate the presence of sleep disordered breathing. Snoring has been correlated with obstructive sleep apnea. Collapse of the soft tissue in the upper airway during an apnea event causes the airway to vibrate, resulting in snoring. Furthermore, snoring may be correlated to hypertension caused by frequent arousals from sleep, reductions in oxygen saturation, increased respiratory effort, and/or increases in thoracic pressure. Thus, detection of frequent snoring may aid in the diagnosis of patients at risk for hypertension and other pathological disorders.
Nighttime snoring may cause an increase in inspiratory effort and reduction in tidal volume, leading to frequent arousals from sleep. Frequent arousals from sleep lead to sleep fragmentation, separate from any underlying disordered breathing. Sleep fragmentation leads to fatigue and sleepiness.